Shape measurement apparatus and method

ABSTRACT

A shape measurement apparatus includes a work stage supporting a target substrate, a pattern-projecting section including a light source, a grating part partially transmitting and blocking light generated by the light source to generate a grating image and a projecting lens part making the grating image on a measurement target of the target substrate, an image-capturing section capturing the grating image reflected by the measurement target of the target substrate, and a control section controlling the work stage, the pattern-projecting section and the image-capturing section, calculating a reliability index of the grating image and phases of the grating image, which is corresponding to the measurement target, and inspecting the measurement target by using the reliability index and the phases. Thus, the accuracy of measurement may be enhanced.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplications No. 2009-44423 filed on May 21, 2009, and No. 2010-7025filed on Jan. 26, 2010, which are hereby incorporated by reference forall purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to a shapemeasurement apparatus and a shape measurement method. More particularly,exemplary embodiments of the present invention relate to a shapemeasurement apparatus and a shape measurement method capable ofenhancing accuracy of measurement.

2. Discussion of the Background

Electronic devices have been developed to have relatively lighter weightand smaller size. Therefore, possibility of defects in these electronicdevices increases and apparatus for inspecting the defects is underdevelopment and improvement.

Recently, the technique for inspecting a three-dimensional shape becomeseffective in various technical fields. In the technique for inspecting athree-dimensional shape, a coordinate measurement machine (CMM), whichdetects three-dimensional shape by a contacting method, was used.However, non-contact method for inspecting a three-dimensional shape byusing optical theories has been under development.

Meadows and Takasaki developed shadow Moire method which is therepresentative non-contact method for inspecting a three-dimensionalshape in 1970. However, the shadow Moire method has a problem that agrating for measurement should be larger than a measurement target insize. In order to solve the above problem, Yoshino developed theprojection Moire technique. Additionally, Kujawinska applied the phaseshifting method which is used for analysis of optical coherence to Moiretechnique for inspecting three-dimensional shape so that the measurementresolution is enhanced and the limitation of Moire pattern is removed.

These techniques for measuring three-dimensional shape may be used forinspection of a printed circuit board, and tries for enhancing accuracyare performed.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention provide a shapemeasurement apparatus capable of measuring a two-dimensional shapetogether with a three-dimensional shape, and enhancing accuracy ofmeasurement.

Exemplary embodiments of the present invention also provide a shapemeasurement method capable of measuring a two-dimensional shape togetherwith a three-dimensional shape, and enhancing accuracy of measurement.

Exemplary embodiments of the present invention also provide a method ofmeasuring a three dimensional shape capable of accurately measuring athree dimensional shape of a measurement target in total areas.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the present invention discloses a shapemeasurement apparatus. The shape measurement apparatus includes a workstage supporting a target substrate, a pattern-projecting sectionincluding a light source, a grating part transmitting and blocking lightgenerated by the light source to generate a grating image and aprojecting lens part making the grating image on a measurement target ofthe target substrate, an image-capturing section capturing the gratingimage reflected by the measurement target of the target substrate, and acontrol section controlling the work stage, the pattern-projectingsection and the image-capturing section, calculating a reliability indexof the grating image and phases of the grating image, which iscorresponding to the measurement target, and inspecting the measurementtarget by using the reliability index and the phases.

The shape measurement apparatus may inspect a surface of a pad throughthe reliability index when the pad is the measurement target. The padmay be to be electrically connected to an external device. Thereliability index may be at least one of an intensity, a visibility anda signal to noise ratio. The control section may determine the pad isbad, when the reliability index is out of a setup value. The shapemeasurement apparatus may further include a subsidiary light source forinspecting the measurement target of the target substrate. The controlsection may determine that the pad is bad when light generated by thesubsidiary light source is reflected by the pad and captured by theimage-capturing section to form a two-dimensional image, and the pad isdetermined as bad in the two-dimensional image, even though thereliability index shows that the pad is good.

Another exemplary embodiment of the present invention discloses a shapemeasurement method. The shape measurement method includes acquiring agrating image reflected by a measurement target, while shifting thegrating image for specific times, acquiring a reliability indexincluding at least one of an intensity, a visibility and a signal tonoise ratio of the grating image by using the grating image, anddetermining a pad for being electrically connected to an external deviceis good when the reliability index is within a setup value, and bad whenthe reliability index is out of the setup value, in case that the pad isthe measurement target.

Still another exemplary embodiment of the present invention discloses amethod of measuring a three dimensional shape. The method includesilluminating grating pattern lights in a plurality of directions onto ameasurement target while changing each of the grating pattern lights byN times and detecting the grating pattern lights reflected by themeasurement target, to acquire N pattern images of the measurementtarget with respect to each direction, extracting a phase {P_(i)(x,y)}and a brightness {A_(i)(x,y)} with respect to each directioncorresponding to each position {i(x,y)} in an X-Y coordinate system fromthe pattern images, extracting a height weight {W_(i)(x,y)} with respectto each direction by using a weight function employing the brightness asa parameter, and calculating a weight height {W_(i)(x,y)·H_(i)(x,y)}with respect to each direction by using a height based on the phase withrespect to each direction and the height weight, and summing weightheights, to produce a height {ΣW_(i)(x,y)·H_(i)(x,y)/ΣW_(i)(x,y)} ateach position.

The brightness may correspond to an average brightness that is obtainedby averaging the detected grating pattern lights.

The weight function may further employ at least one of a visibility andan SNR (signal-to-noise ratio) with respect to each direction extractedfrom the pattern images with respect to each direction as parameters.

The weight function may further employ a measurement scope (λ)corresponding to a grating pitch of each grating pattern light extractedfrom the pattern images with respect to each direction as a parameter.The measurement scope may have at least two values according to thegrating pattern lights.

The weight function may decrease the height weight, as the averagebrightness increases or decreases from a predetermined value. Thepredetermined value may be a mid value of the average brightness.

The weight function may increase the height weight, as the visibility orthe SNR increases.

The weight function may decrease the height weight, as the measurementscope increases.

Extracting the height weight with respect to each direction may includedividing the pattern images into a shadow area, a saturation area and anon-saturation area. The shadow area corresponds to an area, in whichthe average brightness is below a minimum brightness and the visibilityor the SNR is below a minimum reference value, the saturation areacorresponds to an area, in which the average brightness is more than amaximum brightness and the visibility or the SNR is below the minimumreference value, and the non-saturation area corresponds to a remainingarea except the shadow area and the saturation area. The weight functionmay be regarded as ‘0’ to obtain the height weight in the shadow areaand the saturation area. The weight function corresponding to thenon-saturation area may decrease the height weight, as the averagebrightness increases or decreases from a mid value of the averagebrightness, may increase the height weight as the visibility or the SNRincreases, and may decrease the height weight as the measurement scopeincreases.

Sum of the height weights may be equal to 1 {ΣW_(i)(x,y)=1}.

Still another exemplary embodiment of the present invention discloses amethod of measuring a three dimensional shape. The method includesilluminating grating pattern lights in a plurality of directions onto ameasurement target while changing each of the grating pattern lights byN times and detecting the grating pattern lights reflected by themeasurement target, to acquire N pattern images of the measurementtarget with respect to each direction, extracting a phase {P_(i)(x,y)}and a visibility {V_(i)(x,y)} with respect to each directioncorresponding to each position {i(x,y)} in an X-Y coordinate system fromthe pattern images, extracting a height weight {W_(i)(x,y)} with respectto each direction by using a weight function employing the visibility asa parameter, and calculating a weight height {W_(i)(x,y)·H_(i)(x,y)}with respect to each direction by multiplying a height based on thephase by the height weight, and summing weight heights, to produce aheight {ΣW_(i)(x,y)·H_(i)(x,y)/ΣW_(i)(x,y)} at each position.

According to the present invention, two-dimensional shape image may beobtained by using three-dimensional data measured, so that additionaldata for two-dimensional shape image may not be required.

Furthermore, when two-dimensional shape image and three-dimensionalshape image, both of which are measured, are used together, defects ofPCB may be effectively inspected.

Furthermore, when luminance of additional two-dimensional images used,accuracy of inspection may be enhanced.

In addition, average brightness, visibility or SNR, and measurementscope are extracted from the pattern images photographed in eachdirection, and height weight is determined according to the extractedresult, to thereby more accurately measure a height at each position ofmeasurement target in total areas including a shadow area and asaturation, area.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a schematic side view illustrating a shape measurementapparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a schematic top view illustrating a shape measurementapparatus according to another exemplary embodiment of the presentinvention.

FIG. 3 is a top view illustrating a target substrate in FIG. 1.

FIG. 4 is a diagram showing the shape measurement apparatus measuring athree-dimensional image.

FIG. 5 is graphs showing a principle for measuring a two-dimensionalimage.

FIG. 6 is a schematic view illustrating a three dimensional shapemeasurement apparatus used to a method of measuring a three dimensionalshape according to an exemplary embodiment of the present invention.

FIG. 7 is a plan view illustrating a grating pattern image by a gratingpattern light illuminated onto a measurement target in FIG. 6.

FIG. 8 is a plan view illustrating an image measured in the camera whenthe grating pattern light is illuminated onto the measurement targetfrom a right side.

FIG. 9 is a plan view illustrating an image measured in the camera whenthe grating pattern light is illuminated onto the measurement targetfrom a left side.

FIG. 10 is a graph showing a relation between average brightness andweight of the pattern images measured in the camera.

FIG. 11 is a graph showing a relation between visibility or SNR andweight of the pattern images measured in the camera.

FIG. 12 is a graph showing a relation between measurement scope andweight of the pattern images measured in the camera.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention is described more fully hereinafter with referenceto the accompanying drawings, in which example embodiments of thepresent invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the example embodiments set forth herein. Rather, these exampleembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. In the drawings, the sizes and relative sizesof layers and regions may be exaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numerals refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent invention. As used herein, the singular forms “a,” “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Example embodiments of the invention are described herein with referenceto cross-sectional illustrations that are schematic illustrations ofidealized example embodiments (and intermediate structures) of thepresent invention. As such, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, example embodiments of thepresent invention should not be construed as limited to the particularshapes of regions illustrated herein but are to include deviations inshapes that result, for example, from manufacturing. For example, animplanted region illustrated as a rectangle will, typically, haverounded or curved features and/or a gradient of implant concentration atits edges rather than a binary change from implanted to non-implantedregion. Likewise, a buried region formed by implantation may result insome implantation in the region between the buried region and thesurface through which the implantation takes place. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the actual shape of a region of a device andare not intended to limit the scope of the present invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a schematic side view illustrating a shape measurementapparatus according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a shape measurement apparatus 1100 according to anexemplary embodiment of the present invention includes a work stage1130, a pattern-projecting section 1110, an image-capturing section 1150and a control section 1140. Additionally, the shape measurementapparatus 1100 may further include a first subsidiary light source 1160and a second subsidiary light source 1170.

The work stage 1130 support a target substrate 1120 on which ameasurement target A is disposed. Furthermore, the work stage 1130transports the measurement target A along at least one of an x-axisdirection and a y-axis direction. When the work stage 1130 is controlledto transport the target substrate 1120 to a proper position by thecontrol section 1140, the first subsidiary light source 1160 and thesecond subsidiary light source 1170 may radiate a light toward themeasurement target A of the target substrate 1120 to set up a totalmeasuring regions of the target substrate 1120 by using, for example, aidentification mark of the target substrate 1120.

The pattern-projecting section 1110 projecting a grating image towardthe measurement target A. The shape measurement apparatus 1100 mayinclude a plurality of the pattern-projecting sections 1110 disposedsuch that the plurality of pattern-projecting sections 1110 projectgrating images toward the target substrate 1120 with a specific anglewith respect to a normal line of the target substrate 1120. Furthermore,the plurality of pattern-projecting sections 1110 may be disposedsymmetric with respect to the normal line. Each of thepattern-projecting sections 1110 includes a light source 1111, a gratingpart 1112 and a projecting lens part 1113. For example, two thepattern-projecting sections 1110 may be disposed symmetrically withrespect to the measurement target A.

The light source 1111 radiates light toward the measurement target A.

The grating part 1112 makes a grating image by using the light generatedby the light source 1111. The grating part 1112 includes alight-blocking region (not shown) and a light-transmitting region (notshown). The light-blocking region blocks a portion of the lightgenerated by the light source 1111, and the light-transmitting regiontransmits other portion of the light. The grating part 1112 may beformed in various types. For example, the grating part 1112 may beformed by a glass plate on which a grating with a light-blocking regionand a light-transmitting region is patterned. Alternatively, a liquidcrystal display panel may be used as the grating part 1112.

When the glass plate on which the grating with the light-blocking regionand the light-transmitting region is employed as the grating part 1112,the shape measurement apparatus 1100 further includes an actuator (notshown) for minutely transporting the grating part 1112. When a liquidcrystal display panel is employed as the grating part 1112, a gratingpattern may be displayed by the liquid crystal display panel, so thatthe shape measurement apparatus 1100 does to not need the actuator.

The projecting lens part 1113 makes a grating image of the grating part1112 on the measurement target A of the target substrate 1120. Theprojecting lens part 1113 may includes, for example, a plurality oflenses, the grating part 1112 to focus the grating image to be displayedon the measurement target A on the target substrate 1120.

The image-capturing section 1150 receives the grating image reflected bythe measurement target A of the target substrate 1120. Theimage-capturing section 1150 includes, for example, a camera 1151 and acapturing lens part 1152. The grating image reflected by the measurementtarget A passes through the capturing lens part 1152 to be captured bythe camera 1151.

The control section 1140 controls the work stage 1130, thepattern-projecting section 1110 and the image-capturing section 1150,calculates a reliability index of the grating image captured by theimage-capturing section 1150 and phases of the measurement target A, andprocesses the grating image captured by the image-capturing section 1150to measure a two-dimensional shape and a three-dimensional shape. Theprocess for measuring the two-dimensional shape and thethree-dimensional shape, which is performed by the control section 1140,will be explained later in detail.

The control section 1140 inspects the measurement target by using thephase and the reliability index. In detail, the phase may be used formeasuring the three-dimensional shape of the measurement target A, andthe reliability index may be used for determining good or bad regardingthe measurement target. For example, at least one of a signal intensity,a visibility and an SNR (Signal to Noise Ratio) may be used for thereliability index. The signal intensity may to be explained referring toExpression 14 and Expression 15, the visibility may be explainedreferring to Expression 16 or Expression 17, and the SNR means a ratioof or difference between a periodic function generated during theN-bucket algorithm process of filtering images captured by theimage-capturing section 1150 and a real signal. In more detail, the SNRis (visibility*D in Expression 1)/temporal noise D.

When the reliability index is out of a setup value, the control section1140 determines the measurement target A as a bad one.

For example, the control section 1140 determines that the measurementtarget is bad, when the difference between the visibility γ of aspecific region of the shape image obtained through Expression 16 orExpression 17 and the visibility γ of peripheral region is out of therange of the setup value.

Furthermore, one of the first subsidiary light source 1160 and thesecond subsidiary light source 1170 may be used for measuringtwo-dimension shape. In more detail, one of the first subsidiary lightsource 1160 and the second subsidiary light source 1170 radiates lighttoward the measurement target A of the target substrate 1120, andreflected light is captured by the camera 1151 of the image-capturingsection 1150 to generate two-dimensional shape image.

Even when difference of the reliability index is within the setup value,the control section 1140 may determine that the measurement target A isbad when the luminance difference between the specific region of thetwo-dimensional shape image and the peripheral region of thetwo-dimensional shape image is out of another setup value. Furthermore,the control section 1140 may determine that the measurement target A isbad when the luminance of a specific region of the measurement target Ais out of another setup value.

For example, even when the difference between the visibility γ of aspecific region obtained through Expression 16 or Expression 17 and thevisibility γ of a peripheral region is within the setup value, thecontrol section 1140 determines that the measurement target A is badwhen luminance difference or intensity difference between the specificregion and the peripheral region of the two-dimensional image obtainedthrough the first subsidiary light source 1160 or the second subsidiarylight source 1170 is out of another setup value.

The control section 1140 inspects the two-dimensional shape and thethree-dimensional shape of a region of interest (ROI) in fields of view(FOV) in sequence.

FIG. 2 is a schematic top view illustrating a shape measurementapparatus according to another exemplary embodiment of the presentinvention. The shape measurement apparatus according to the presentembodiment is substantially same except for the pattern-projectingsection of the shape measurement apparatus 1100 in FIG. 1. Therefore,same reference numerals will be used for the same elements and anyfurther explanation will be omitted.

Referring to FIG. 2, the shape measurement apparatus according to thepresent embodiment includes a plurality of pattern-projecting sections1110, each of which has a grating part 1112. The plurality ofpattern-projecting sections 1110 is arranged at apexes of a polygon. InFIG. 2, four pattern-projecting sections 1110 are arranged at apexes ofa square. However, the plurality of pattern-projecting sections 1110 maybe arranged at apexes of hexagon, octagon, etc.

When the grating image is captured only at one side, exactthree-dimensional shape may be obtained since the measurement target Ais a protrusion so that the grating image may be arrive at the otherside. Therefore, the grating image may be captured at both sidesopposite to each other in order to obtain the exact three-dimensionalshape.

For example, when the measurement target A has rectangular shape, thecontrol section 1140 may turn on two pattern-projecting sections 1110disposed opposite to each other. When the shape of the measurementtarget A, which is grasped by the control section 1140, is complex, thecontrol section 1140 may turn on more than two pattern-projectingsections 1110.

FIG. 3 is a top view illustrating a target substrate in FIG. 1.

Referring to FIG. 3, the target substrate 1120 such as a printed circuitboard (PCB) includes, for example, a pad region 1121 (or fan out region)and a device-mounting region 1122.

The pad region 1121 is a region in which a pad for electrical connectingis formed, and the device-mounting region 1122 is a region on which adevice is mounted.

A device is mounted on the device-mounting region 1122 through solderpaste. When the shape or the amount of the solder paste is not properlycontrolled, the device may be electrically connected with other devicesto induce mal-function. Therefore, in order to check that the shape orthe amount of the solder paste is property controlled, the shape and theheight of the solder paste is measured to obtain three-dimensional shapeof the solder paste.

Furthermore, the pad region 1121 should be checked for preventingelectrical short with other pad region. In this case, two-dimensionalshape obtained through Expression 14 or Expression 15 may be used forchecking electrical short between the pad regions.

Additionally, the pad region 1121 should have flat surface. When the padregion 1121 is scratched, the pad region may induce a bad connectionwith a device. Therefore, the surface inspection of the pad region 1121is very important.

For the surface inspection, the reliability index of the pad region 1121is inspected. When the reliability index of a specific region is out ofthe setup value, the pad region 1121 is determined to be bad. Even whenthe reliability index of the specific region is within the setup value,a luminance difference of a specific region and a peripheral region in atwo dimensional image obtained by using one of the first subsidiarylight source 1160 and the second subsidiary light source 1170 in FIG. 1is out of another setup value, the pad is determined to be bad since thepad has a scratch.

The pad region 1121 is a flat metal surface, so that the amount of lightreflected by the pad region 1121 and captured by the camera 1151 of theimage-capturing section 1150 in FIG. 1 may be saturated. Therefore, ashifted phase value may be measured. However the reliability index maybe measured. Therefore, the pad region 1121 may be inspected by usingthe reliability index even when the amount of the light reflected by thepad region 1121 is saturated. Furthermore, the reliability index of eachpattern-projecting section 1110 may be used as a weight value for theheight measured by the each pattern-projecting section 1110.

Hereinbefore, the shape measurement apparatuses according to the presentembodiments are explained. The shape measurement method according to thepresent embodiment is substantially the same as that of the shapemeasurement apparatus. That is, According to shape measurement method ofthe present invention, grating images reflected by a measurement targetare obtained while shifting a grating, several times. Then, thereliability index of the grating images is obtained. When thereliability index is within the setup value, the measurement target isdetermined to be good, and when the reliability index is out of thesetup value, the measurement target is determined to be bad.Furthermore, two-dimensional shape image of the measurement target maybe obtained, and even when the reliability index of the pad is withinthe setup value, the pad may be determined to be bad when a luminancedifference between a specific region and a peripheral region of thetwo-dimensional shape image is out of a specific value.

FIG. 4 is a diagram showing the shape measurement apparatus measuring athree-dimensional image.

The grating image is radiated onto the target substrate 1120 in FIG. 1.Then, intensity I of images reflected by the target substrate 1120 andcaptured by the image-capturing section 1150 is expressed as thefollowing Expression 1 corresponding to Moire equation.

$\begin{matrix}{I = {D\left\lbrack {1 + {\gamma\;{\cos\left( \frac{2\pi\; h}{\Lambda} \right)}}} \right\rbrack}} & {{Expression}\mspace{14mu} 1}\end{matrix}$

wherein I is intensity captured by the image-capturing section 1150, Dis signal intensity (or a function of DC light intensity (or lightsource intensity) and reflectivity), γ is visibility (a function ofreflectivity and period of grating), Λ is Moire equivalence period (afunction of magnification, the period of grating and radiation angle θ).

In Expression 1 intensity I is a function of height h, so that height hmay be obtained by using intensity I.

When the phase of grating is shifted and reflected image is captured bythe image-capturing section 1150 in FIG. 1, Expression 1 may beexpressed as Expression 2.

$\begin{matrix}{I_{k} = {D\left\lbrack {1 + {\gamma\;{\cos\left( {\frac{2\pi\; h}{\Lambda} + \delta_{k}} \right)}}} \right\rbrack}} & {{Expression}\mspace{14mu} 2}\end{matrix}$

where δk is phase shift, and 2πh/Λ corresponds to a phase Φcorresponding to the measurement target.

In order to obtain height h by using Expression 2, at least three phaseshifts are required.

For example, when three phase shifts are applied (3-bucket algorithm),the height h may be obtained as follows. In Expression 2, zero radian isapplied as δ1 to obtain I1, and then Expression 2 is expressed asfollowing Expression 3.

$\begin{matrix}{I_{1} = {D\left\lbrack {1 + {\gamma\;{\cos\left( \frac{2\pi\; h}{\Lambda} \right)}}} \right\rbrack}} & {{Expression}\mspace{14mu} 3}\end{matrix}$

In Expression 2, 2π/3 radian is applied as δ2 to obtain I2, and thenExpression 2 is expressed as following Expression 4.

$\begin{matrix}{I_{2} = {{D\left\lbrack {1 + {\gamma\;{\cos\left( {\frac{2\pi\; h}{\Lambda} + \frac{2\pi}{3}} \right)}}} \right\rbrack} = {D\left\lbrack {1 - {\gamma\left( {{{\cos\left( \frac{2\pi\; h}{\Lambda} \right)}\left( \frac{1}{2} \right)} + {{\sin\left( \frac{2\pi\; h}{\Lambda} \right)}\left( \frac{\sqrt{3}}{2} \right)}} \right)}} \right\rbrack}}} & {{Expression}\mspace{14mu} 4}\end{matrix}$

In Expression 2, 4π/3 radian is applied as δ3 to obtain I3, and thenExpression 2 is expressed as following Expression 5.

$\begin{matrix}{I_{3} = {{D\left\lbrack {1 + {{\gamma cos}\left( {\frac{2\pi\; h}{\Lambda} + \frac{4\pi}{3}} \right)}} \right\rbrack} = {D\left\lbrack {1 - {\gamma\left( {{{\cos\left( \frac{2\pi\; h}{\Lambda} \right)}\left( \frac{- 1}{2} \right)} - {{\sin\left( \frac{2\pi\; h}{\Lambda} \right)}\left( \frac{\sqrt{3}}{2} \right)}} \right)}} \right\rbrack}}} & {{Expression}\mspace{14mu} 5}\end{matrix}$

By using Expression 3, Expression 4 and Expression 5, followingExpression 6 is obtained.

$\begin{matrix}{\frac{\left( {I_{3} - I_{2}} \right)}{{2I_{1}} - I_{3} - I_{2}} = {\tan\left( \frac{2\pi\; h}{\Lambda} \right)}} & {{Expression}\mspace{14mu} 6}\end{matrix}$

By using Expression 6, the height h may be obtained as followingExpression 7.

$\begin{matrix}{h = {\frac{\Lambda}{2\pi}{\tan^{- 1}\left\lbrack \frac{\sqrt{3}\left( {I_{3} - I_{2}} \right)}{{2I_{1}} - I_{3} - I_{2}} \right\rbrack}}} & {{Expression}\mspace{14mu} 7}\end{matrix}$

For example, when four phase shifts are applied (4-bucket algorithm),the height h may be obtained as follows. In Expression 2, zero radian isapplied as δ1 to obtain I1, and then Expression 2 is expressed asfollowing Expression 8.

$\begin{matrix}{I_{1} = {D\left\lbrack {1 + {{\gamma cos}\left( \frac{2\pi\; h}{\Lambda} \right)}} \right\rbrack}} & {{Expression}\mspace{14mu} 8}\end{matrix}$

In Expression 2, π/2 radian is applied as δ2 to obtain I2, and thenExpression 2 is expressed as following Expression 9.

$\begin{matrix}{I_{2} = {{D\left\lbrack {1 + {{\gamma cos}\left( {\frac{2\pi\; h}{\Lambda} + \frac{\pi}{2}} \right)}} \right\rbrack} = {D\left\lbrack {1 - {{\gamma sin}\left( \frac{2\pi\; h}{\Lambda} \right)}} \right\rbrack}}} & {{Expression}\mspace{14mu} 9}\end{matrix}$

In Expression 2, π radian is applied as δ3 to obtain I3, and thenExpression 2 is expressed as following Expression 10.

$\begin{matrix}{I_{3} = {{D\left\lbrack {1 + {{\gamma cos}\left( {\frac{2\pi\; h}{\Lambda} + \pi} \right)}} \right\rbrack} = {D\left\lbrack {1 - {{\gamma cos}\left( \frac{2\pi\; h}{\Lambda} \right)}} \right\rbrack}}} & {{Expression}\mspace{14mu} 10}\end{matrix}$

In Expression 2, 3π/2 radian is applied as δ4 to obtain I4, and thenExpression 2 is expressed as following Expression 11.

$\begin{matrix}{I_{4} = {{D\left\lbrack {1 + {{\gamma cos}\left( {\frac{2\pi\; h}{\Lambda} + \frac{3\pi}{2}} \right)}} \right\rbrack} = {D\left\lbrack {1 + {{\gamma sin}\left( \frac{2\pi\; h}{\Lambda} \right)}} \right\rbrack}}} & {{Expression}\mspace{14mu} 11}\end{matrix}$

By using Expression 8, Expression 9, Expression 10 and Expression 11,following Expression 12 is obtained.

$\begin{matrix}{\frac{I_{4} - I_{2}}{I_{1} - I_{3}} = {\tan\left( \frac{2\pi\; h}{\Lambda} \right)}} & {{Expression}\mspace{14mu} 12}\end{matrix}$

By using Expression 12, the height h may be obtained as followingExpression 13.

$\begin{matrix}{h = {\frac{\Lambda}{2\pi}{\tan^{- 1}\left\lbrack \frac{\left( {I_{4} - I_{2}} \right)}{\left( {I_{1} - I_{3}} \right)} \right\rbrack}}} & {{Expression}\mspace{14mu} 13}\end{matrix}$

When grating image is radiated onto the measurement target and capturedthe reflected image while shifting the grading, three-dimensional shapeof the measurement target may be obtained by using Expression 7 orExpression 13.

FIG. 5 is graphs showing a principle for measuring a two-dimensionalimage.

Arithmetic mean value lave of I1 I2, I3 and I4 may be obtained asfollowing Expression 14.

$\begin{matrix}{I_{ave} = {\frac{I_{1} + I_{2} + I_{3} + I_{4}}{4} = D}} & {{Expression}\mspace{14mu} 14}\end{matrix}$

As shown in Expression 14, effect of grating may be offset whenaveraged, so that two-dimensional shape image may be obtained.

In case of 3-bucket algorithm, arithmetic mean value Iave of I1 I2 andI3 in Expressions 3, 4 and 5, respectively may be expressed as followingExpression 15.

$\begin{matrix}{I_{ave} = {\frac{I_{1} + I_{2} + I_{3}}{3} = D}} & {{Expression}\mspace{14mu} 15}\end{matrix}$

On the other hand, the visibility γ in Expression 2 may be expressed asfollowing Expression 16 by using Expression 3, 4, 5 and 15 in case of3-bucket algorithm.

$\begin{matrix}{\gamma = \frac{\sqrt{\left( {{2I_{1}} - I_{2} - I_{3}} \right)^{2} + {3\left( {I_{2} - I_{3}} \right)^{2}}}}{\left( {I_{1} + I_{2} + I_{3}} \right)}} & {{Expression}\mspace{14mu} 16}\end{matrix}$

The visibility γ in Expression 2 may be expressed as followingExpression 17 by using Expression 8, 9, 10, 11 and 14 in case of4-bucket algorithm.

$\begin{matrix}{\gamma = {2\frac{\sqrt{\left( {I_{1} - I_{3}} \right)^{2} + \left( {I_{2} - I_{4}} \right)^{2}}}{\left( {I_{1} + I_{2} + I_{3} + I_{4}} \right)}}} & {{Expression}\mspace{14mu} 17}\end{matrix}$

According to the present invention, two-dimensional shape image may beobtained by using three-dimensional data measured, so that additionaldata for two-dimensional shape image may be not required.

Furthermore, when two-dimensional shape image and three-dimensionalshape image, both of which are measured, are used together, defects ofPCB may be effectively inspected.

FIG. 6 is a schematic view illustrating a three dimensional shapemeasurement apparatus used to a method of measuring a three dimensionalshape according to an exemplary embodiment of the present invention.

Referring to FIG. 6, a three dimensional shape measurement apparatusused to a method of measuring a three dimensional shape according to anexemplary embodiment of the present invention may include a measurementstage section 100, an image photographing section 200, first and secondillumination sections 300 and 400, an image acquiring section 500, amodule control section 600 and a central control section 700.

The measurement stage section 100 may include a stage 110 supporting ameasurement target 10 and a stage transfer unit 120 transferring thestage 110. In an exemplary embodiment, according as the measurementtarget 10 moves with respect to the image photographing section 200 andthe first and second illumination sections 300 and 400 by the stage 110,a measurement location may be changed in the, measurement target 10.

The image photographing section 200 is disposed over the stage 110 toreceive light reflected by the measurement target 10 and measure animage of the measurement target 10. That is, the image photographingsection 200 receives the light that exits the first and secondillumination sections 300 and 400 and is reflected by the measurementtarget 10, and photographs a plan image of the measurement target 10.

The image photographing section 200 may include a camera 210, an imaginglens 220, a filter 230 and a lamp 240. The camera 210 receives the lightreflected by the measurement target 10 and photographs the plan image ofthe measurement target 10. The camera 210 may include, for example, oneof a CCD camera and a CMOS camera. The imaging lens 220 is disposedunder the camera 210 to image the light reflected by the measurementtarget 10 on the camera 210. The filter 230 is disposed under theimaging lens 220 to filter the light reflected by the measurement target10 and provide the filtered light to the imaging lens 220. The filter230 may include, for example, one of a frequency filter, a color filterand a light intensity control filter. The lamp 240 may be disposed underthe filter 230 in a circular shape to provide the light to themeasurement target 10, so as to photograph a particular image such as atwo-dimensional shape of the measurement target 10.

The first illumination section 300 may be disposed, for example, at aright side of the image photographing section 200 to be inclined withrespect to the stage 110 supporting the measurement target 10. The firstillumination section 300 may include a first light source unit 310, afirst grating unit 320, a first grating transfer unit 330 and a firstcondensing lens 340. The first light source unit 310 may include a lightsource and at least one lens to generate light, and the first gratingunit 320 is disposed under the first light source unit 310 to change thelight generated by the first light source unit 310 into a first gratingpattern light having a grating pattern. The first grating transfer unit330 is connected to the first grating unit 320 to transfer the firstgrating unit 320, and may include, for example, one of a piezoelectrictransfer unit and a fine linear transfer unit. The first condensing lens340 is disposed under the first grating unit 320 to condense the firstgrating pattern light exiting the first grating unit 320 on themeasurement target 10.

For example, the second illumination section 400 may be disposed at aleft side of the image photographing section 200 to be inclined withrespect to the stage 110 supporting the measurement target 10. Thesecond illumination section 400 may include a second light source unit410, a second grating unit 420, a second grating transfer unit 430 and asecond condensing lens 440. The second illumination section 400 issubstantially the same as the first illumination section 300 describedabove, and thus any further description will be omitted.

When the first grating transfer unit 330 sequentially moves the firstgrating unit 320 by N times and N first grating pattern lights areilluminated onto the measurement target 10 in the first illuminationsection 300, the image photographing section 200 may sequentiallyreceive the N first grating pattern lights reflected by the measurementtarget 10 and photograph N first pattern images. In addition, when thesecond grating transfer unit 430 sequentially moves the second gratingunit 420 by N times and N first grating pattern lights are illuminatedonto the measurement target 10 in the second illumination section 400,the image photographing section 200 may sequentially receive the Nsecond grating pattern lights reflected by the measurement target 10 andphotograph N second pattern images. The ‘N’ is a natural number, and forexample may be four.

In an exemplary embodiment, the first and second illumination sections300 and 400 are described as an illumination apparatus generating thefirst and second grating pattern lights. Alternatively, the illuminationsection may be more than or equal to three. In other words, the gratingpattern light may be illuminated onto the measurement target 10 invarious directions, and various pattern images may be photographed. Forexample, when three illumination sections are disposed in an equilateraltriangle form with the image photographing section 200 being the centerof the equilateral triangle form, three grating pattern lights may beilluminated onto the measurement target 10 in different directions. Forexample, when four illumination sections are disposed in a square formwith the image photographing section 200 being the center of the squareform, four grating pattern lights may be illuminated onto themeasurement target 10 in different directions.

The image acquiring section 500 is electrically connected to the camera210 of the image photographing section 200 to acquire the pattern imagesfrom the camera 210 and store the acquired pattern images. For example,the image acquiring section 500 may include an image system thatreceives the N first pattern images and the N second pattern imagesphotographed in the camera 210 and stores the images.

The module control section 600 is electrically connected to themeasurement stage section 100, the image photographing section 200, thefirst illumination section 300 and the second illumination section 400,to control the measurement stage section 100, the image photographingsection 200, the first illumination section 300 and the secondillumination section 400. The module control section 600 may include,for example, an illumination controller, a grating controller and astage controller. The illumination controller controls the first andsecond light source units 310 and 410 to generate light, and the gratingcontroller controls the first and second grating transfer units 330 and430 to move the first and second grating units 320 and 420. The stagecontroller controls the stage transfer unit 120 to move the stage 110 inan up-and-down motion and a left-and-right motion.

The central control section 700 is electrically connected to the imageacquiring section 500 and the module control section 600 to control theimage acquiring section 500 and the module control section 600.Particularly, the central control section 700 receives the N firstpattern images and the N second pattern images from the image system ofthe image acquiring section 500 to process the images, so that threedimensional shape of the measurement target may be measured. Inaddition, the central control section 700 may control an illuminationcontroller, a grating controller and a stage controller of the modulecontrol section 600. Thus, the central control section may include animage processing board, a control board and an interface board.

Hereinafter, a method of measuring the measurement target 10 formed on aprinted circuit board by using the above described three dimensionalshape measurement apparatus will be described in detail. It will bedescribed employing a solder as an example of the measurement target 10.

FIG. 7 is a plan view illustrating a grating pattern image by a gratingpattern light illuminated onto a measurement target in FIG. 6.

Referring to FIGS. 6 and 7, when the grating pattern light from one ofthe plurality of the illumination sections is illuminated onto themeasurement target 10, a grating pattern image is formed on themeasurement target 10. The grating pattern image includes a plurality ofgrating patterns, and in the present embodiment, an interval between thegrating patterns, i.e., a grating pitch is defined as a measurementscope λ.

The measurement scope λ may be the same irrespective of sorts of thegrating pattern lights, but alternatively, may be different from eachother according to sorts of the grating pattern lights. The measurementscope λ may have at least two values according to sorts of the gratingpattern lights. For example, the grating pattern image by the firstgrating pattern light generated from the first illumination section 300may have grating patterns of a first measurement scope, and the gratingpattern image by the second grating pattern light generated from thesecond illumination section 400 may have grating patterns of a secondmeasurement scope different from the first measurement scope.

FIG. 8 is a plan view illustrating an image measured in the camera whenthe grating pattern light is illuminated onto the measurement targetfrom a right side. FIG. 9 is a plan view illustrating an image measuredin the camera when the grating pattern light is illuminated onto themeasurement target from a left side. In the images of FIGS. 8 and 9, arelative amount with respect to brightness (luminance) is just shown,and the grating pattern is omitted.

Referring to FIGS. 6, 8 and 9, when the grating pattern light from oneof the plurality of the illumination sections is illuminated onto themeasurement target 10, an image photographed in the camera 210 mayinclude a shadow area that is relatively dark and a saturation area thatis relatively bright.

For example, as shown in FIG. 8, when the grating pattern light isilluminated onto the measurement target 10 from right side, typically,the saturation area is formed at a right portion of the measurementtarget 10, and the shadow area is formed at a left portion of themeasurement target 10. In contrast, as shown in FIG. 9, when the gratingpattern light is illuminated onto the measurement target 10 from leftside, typically, the saturation area is formed at a left portion of themeasurement target 10, and the shadow area is formed at a right portionof the measurement target 10.

Hereinafter, referring again to FIGS. 6 to 8, a method of measuring athree dimensional shape according to the present embodiment will bedescribed based on the above described explanation.

Firstly, the grating pattern lights generated in a plurality ofdirections are sequentially illuminated onto the measurement target 10disposed on the stage 110, and the grating pattern lights reflected bythe measurement target 10 are sequentially detected in the camera 210 toacquire a plurality of pattern images.

Particularly, each of the grating pattern lights is moved aside andilluminated onto the measurement target 10 by N times, for example,three times or four times, to acquire N pattern images of themeasurement target 10 for each of the directions. For example, as shownin FIG. 6, when the first and second grating pattern lights generatedfrom the first and second illumination sections 300 and 400 areilluminated onto the measurement target 10, N first pattern images and Nsecond pattern images may be acquired.

Then, N brightness degrees {I^(i) ₁, I^(i) ₂, . . . , I^(i) _(N)} ateach position {i(x,y)} in an X-Y coordinate system, and the measurementscope λ as shown in FIG. 7 are extracted from N pattern images withrespect to each direction. Thereafter, phase {P_(i)(x,y)}, brightness{A_(i)(x,y)} and visibility {V_(i)(x,y)} with respect to each directionare calculated from the N brightness degrees {I^(i) ₁, I^(i) ₂, . . . ,I^(i) _(N)}. The phase {P_(i)(x,y)}, the brightness {A_(i)(x,y)} the andthe visibility {V_(i)(x,y)} with respect to each direction may becalculated by using an N-bucket algorithm. In addition, the brightness{A_(i)(x,y)} may be an average brightness that is obtained by averagingthe detected grating pattern lights. Thus, hereinafter, the brightness{A_(i)(x,y)} will be called “average brightness {A_(i)(x,y)}”.

For example, when N is 3, three brightness degrees {I^(i) ₁, I^(i) ₂,I^(i) ₃} are extracted from three pattern images with respect to eachdirection, and phase {P_(i)(x,y)}, average brightness {A_(i)(x,y)} andvisibility {V_(i)(x,y)} may be calculated as shown in the followingequations through a three-bucket algorithm. In the following equations,B_(i)(x,y) indicates an amplitude of an image signal (brightness signal)in three pattern images with respect to each direction. I^(i) ₁corresponds to “a+b cos(Φ)”, I^(i) ₂ corresponds to “a+b cos(φ+2π/3)”,and I^(i) ₃ corresponds to “a+b cos(φ+4π/3)”.

${P_{i}\left( {x,y} \right)} = {\tan^{- 1}\frac{\sqrt{3}\left( {I_{3}^{i} - I_{2}^{i}} \right)}{{2I_{1}^{i}} - I_{2}^{i} - I_{3}^{i}}}$${A_{i}\left( {x,y} \right)} = \frac{I_{1}^{i} + I_{2}^{i} + I_{3}^{i}}{3}$${V_{i}\left( {x,y} \right)} = {\frac{B_{i}}{A_{i}} = \frac{\sqrt{\left( {{2I_{1}^{i}} - I_{2}^{i} - I_{3}^{i}} \right)^{2} + {3\left( {I_{2}^{i} - I_{3}^{i}} \right)^{2}}}}{\left( {I_{1}^{i} + I_{2}^{i} + I_{3}^{i}} \right)}}$

In contrast, for example, when N is 4, four brightness degrees {I^(i) ₁,I^(i) ₂, I^(i) ₃, I^(i) ₄} are extracted from four pattern images withrespect to each direction, and phase {P_(i)(x,y)}, average brightness{A_(i)(x,y)} and visibility {V_(i)(x,y)} may be calculated as shown inthe following equations through a four-bucket algorithm. In thefollowing equations, B_(i)(x,y) indicates an amplitude of an imagesignal (brightness signal) in four pattern images with respect to eachdirection corresponds to “a+b cos(Φ)”, I^(i) ₂ corresponds to “a+bcos(φ+π/2)”, and I^(i) ₃ corresponds to “a+b cos(φ+π)” and I^(i) ₄corresponds to “a+b cos(φ+3π/2)”.

${P_{i}\left( {x,y} \right)} = {\tan^{- 1}\frac{I_{4}^{i} - I_{2}^{i}}{I_{1}^{i} - I_{3}^{i}}}$${A_{i}\left( {x,y} \right)} = \frac{I_{1}^{i} + I_{2}^{i} + I_{3}^{i} + I_{4}^{i}}{4}$${V_{i}\left( {x,y} \right)} = {\frac{B_{i}}{A_{i}} = \frac{2\sqrt{\left( {I_{1}^{i} - I_{3}^{i}} \right)^{2} + \left( {I_{2}^{i} - I_{4}^{i}} \right)^{2}}}{\left( {I_{1}^{i} + I_{2}^{i} + I_{3}^{i} + I_{4}^{i}} \right)}}$

In an exemplary embodiment, a signal-to-noise ratio (SNR) may becalculated and used in place of the visibility {V_(i)(x,y)} or togetherwith the visibility {V_(i)(x,y)}. The SNR Indicates a ratio of an imagesignal S to a noise signal N (S/N) in N pattern images with respect toeach direction.

Thereafter, height {H_(i)(x,y)} with respect to each direction iscalculated from the phase {P_(i)(x,y)} with respect to each direction bythe following equation. In the following equation, k_(i)(x,y) is aphase-to-height conversion scale that indicates a conversion ratiobetween a phase to and a height.H _(i)(x,y)=k _(i)(x,y)·P _(i)(x,y)

Height weight {W_(i)(x,y)} with respect to each direction is calculatedby using at least one of the average brightness {A_(i)(x,y)}, thevisibility {V_(i)(x,y)} and the measurement scope λ. The height weight{W_(i)(x,y)} with respect to each direction may be obtained as followsby a weight function {f(A_(i), V_(i)λ)} having parameters of, forexample, the average brightness {A_(i)(x,y)}, the visibility{V_(i)(x,y)} and the measurement scope(λ). Sum of the height weights inthe total directions may be 1 {ΣW_(i)(x,y)=1}.W _(i)(x,y)=f(A _(i) ,V _(i),λ)

Then, the height {H_(i)(x,y)} with respect to each direction ismultiplied by the height weight {W_(i)(x,y)} with respect to eachdirection to calculate weight height {W_(i)(x,y)·H_(i)(x,y)} withrespect to each direction. Thereafter, the weight heights in the totaldirections are summed and divided by the sum of the height weights{ΣW_(i)(x,y)} to calculate height {ΣW_(i)(x,y)·H_(i)(x,y)/ρW_(i)(x,y)}at each position.

Then, the three dimensional shape of the measurement target 10 may beaccurately measured by combining the heights according to positionscalculated as the above.

Hereinafter, relations between the height weight {W_(i)(x,y)} withrespect to each direction and characteristics of the weight function{f(A_(i), V_(i),λ)}, i.e., the average brightness {A_(i)(x,y)}, thevisibility {V_(i)(x,y)} or the SNR, and the measurement scope λ, will bedescribed in detail.

FIG. 10 is a graph showing a relation between average brightness andweight of the pattern images measured in the camera.

Referring to FIG. 10, firstly, when the average brightness {A_(i)(x,y)}increases or decreases from a predetermined value that is set inadvance, the weight function {f(A_(i), V_(i),λ)} may act on the heightweight {W_(i)(x,y)} to decrease. In other words, when the averagebrightness {A_(i)(x,y)} has the predetermined value, the height weight{W_(i)(x,y)} has relatively the greatest value, and as the averagebrightness {A_(i)(x,y)} becomes distant from the predetermined value,the height weight {W_(i)(x,y)} may decrease. The predetermined value maybe set when determining a three dimensional condition by using aspecimen stone or may be arbitrarily set by a user. However, thepredetermined value may preferably be an average value, i.e., a midvalue of the average brightness {A_(i)(x,y)}.

FIG. 11 is a graph showing a relation between visibility or SNR andweight of the pattern images measured in the camera.

Referring to FIG. 11, thereafter, when the visibility {V_(i)(x,y)} orthe SNR increases, the weight function {f(A_(i), V_(i),λ)} may act onthe height weight to increase. In other words, as the visibility{V_(i)(x,y)} or the SNR slowly increases, the height weight {W_(i)(x,y)}may also slowly increase.

FIG. 12 is a graph showing a relation between measurement scope andweight of the pattern images measured in the camera.

Referring to FIG. 12, then, when the measurement scope λ increases, theweight function {f(A_(i), V_(i),λ)} may act on the height weight{W_(i)(x,y)} to decrease. In other words, as the measurement scope λslowly increases, the height weight {W_(i)(x,y)} may slowly decrease.

Referring again to FIGS. 7, 10 and 11, the N pattern images with respectto each direction are divided into a shadow area, a saturation area andnon-saturation area, and different height weight {W_(i)(x,y)} may begiven according to each area. In the shadow area, the average brightness{A_(i)(x,y)} is below a minimum brightness A1, and the visibility{V_(i)(x,y)} or the SNR is below a minimum reference value Vmin. In thesaturation area, the average brightness {A_(i)(x,y)} is more than amaximum brightness A2, and the visibility or the SNR is below theminimum reference value Vmin. The non-saturation area corresponds to aremaining area except the shadow area and the saturation area.

Firstly, in the shadow area and the saturation area, the weight function{f(A_(i), V_(i),λ)} is regarded as ‘0’ to obtain the height weight{W_(i)(x,y)}. In other words, in the shadow area and the saturationarea, the height weight {W_(i)(x,y)} is determined as ‘0’.

Then, in the non-saturation area, as shown in FIGS. 10 to 12, the weightfunction {f(A_(i), V_(i),λ)} may decrease the height weight {W_(i)(x,y)}when the average brightness {A_(i)(x,y)} increases or decreases from themid value, increase the height weight {W_(i)(x,y)} when the visibility{V_(i)(x,y)} or the SNR increases, and decrease the height weight{W_(i)(x,y)} when the measurement scope λ increases.

In contrast, in the non-saturation area, the weight function {f(A_(i),V_(i)λ)} may be regarded as the same to obtain the height weight{W_(i)(x,y)}. For example, when height weights with respect to fourdirections in the non-saturation area are called for first, second,third and fourth height weights W₁, W₂, W₃ and W₄, all of the first,second, third and fourth height weights W₁, W₂, W₃ and W₄ may bedetermined as ‘¼’.

According to the present embodiment, the average brightness{A_(i)(x,y)}, the visibility {V_(i)(x,y)} or SNR, and the measurementscope λ are extracted from the N pattern images photographed in eachdirections, and the height weight {W_(i)(x,y)} is determined accordingto the extraction result, thereby accurately measuring the heightaccording to each position of the measurement target 10 in all theareas.

Especially, the N pattern images with respect to each direction aredivided into the shadow area, the saturation area and the non-saturationarea, and different height weight {W_(i)(x,y)} is given according toeach area, to thereby prevent reliability reduction for the height inthe shadow area and the saturation area. In other words, the heightweight {W_(i)(x,y)} is given as relatively low value, for example, ‘0’in the shadow area and the saturation area, the height weight{W_(i)(x,y)} is given as relatively great value in the non-saturationarea, thereby compensating for adverse effect incurred from the shadowarea and the saturation area to more accurately measure a threedimensional shape of the measurement target.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of measuring a three dimensional shape comprising: illuminating grating pattern lights in a plurality of directions onto a measurement target while changing each of the grating pattern lights by N times and detecting the grating pattern lights reflected by the measurement target, to acquire N pattern images of the measurement target with respect to each direction; extracting a phase, a brightness and a visibility with respect to each direction corresponding to each position from the pattern images; extracting a height weight with respect to each direction by using a weight function employing the brightness and the visibility as a parameter; calculating a weight height with respect to each direction by using a height based on the phase with respect to each direction and the height weight; and calculating a height at each position by using weight heights with respect to the plurality of directions, wherein the visibility is an amplitude of brightness signal divided by an average brightness.
 2. The method of claim 1, wherein the brightness corresponds to an average brightness that is obtained by averaging the detected grating pattern lights.
 3. The method of claim 2, wherein the weight function further employs at least one of a visibility and an SNR (signal-to-noise ratio) with respect to each direction extracted from the pattern images with respect to each direction as parameters.
 4. The method of claim 3, wherein the weight function further employs a measurement scope (X) corresponding to a grating pitch of each grating pattern light extracted from the pattern images with respect to each direction as a parameter.
 5. The method of claim 4, wherein the measurement scope has at least two values according to the grating pattern lights.
 6. The method of claim 4, wherein the weight function decreases the height weight, as the measurement scope increases.
 7. The method of claim 4, wherein extracting the height weight with respect to each direction comprising dividing the pattern images into a shadow area, a saturation area and a non-saturation area, and wherein the shadow area corresponds to an area, in which the average brightness is below a minimum brightness and the visibility or the SNR is below a minimum reference value, the saturation area corresponds to an area, in which the average brightness is more than a maximum brightness and the visibility or the SNR is below the minimum reference value, and the non-saturation area corresponds to a remaining area except the shadow area and the saturation area.
 8. The method of claim 7, wherein the weight function is regarded as ‘0’ to obtain the height weight in the shadow area and the saturation area.
 9. The method of claim 8, wherein the weight function corresponding to the non-saturation area decreases the height weight, as the average brightness increases or decreases from a mid value of the average brightness, increases the height weight as the visibility or the SNR increases, and decreases the height weight as the measurement scope increases.
 10. The method of claim 3, wherein the weight function decreases the height weight, as the average brightness increases or decreases from a predetermined value.
 11. The method of claim 10, wherein the predetermined value is a mid value of the average brightness.
 12. The method of claim 3, wherein the weight function increases the height weight, as the visibility or the SNR increases.
 13. The method of claim 1, wherein sum of the height weights with respect to the plurality of directions is equal to 1, and wherein the height at each position is calculated by summing the weight heights with respect to the plurality of directions.
 14. The method of claim 1, further comprising measuring a three dimensional shape by combining the height at each position.
 15. A method of measuring a three dimensional shape comprising: illuminating grating pattern lights in a plurality of directions onto a measurement target while changing each of the grating pattern lights by N times and detecting the grating pattern lights reflected by the measurement target, to acquire N pattern images of the measurement target with respect to each direction; extracting a phase and a brightness with respect to each direction corresponding to each position from the pattern images; extracting a height weight with respect to each direction by using a weight function employing the brightness as a parameter, wherein the pattern images are divided into a shadow area, a saturation area and a non-saturation area at least based on the brightness with respect to each direction, and the height weight with respect to each direction is determined according to the shadow area, the saturation area and the non-saturation area; calculating a weight height with respect to each direction by multiplying a height based on the phase by the height weight, and calculating a height at each position by using weight heights with respect to the plurality of directions, wherein the brightness corresponds to an average brightness that is obtained by averaging the detected grating pattern lights, wherein the weight function further employs a visibility with respect to each direction extracted from the pattern images with respect to each direction as parameters, and wherein the visibility is an amplitude of brightness signal divided by an average brightness.
 16. The method of claim 15, wherein the shadow area corresponds to an area, in which the average brightness is below a minimum brightness and the visibility is below a minimum reference value, the saturation area corresponds to an area, in which the average brightness is more than a maximum brightness and the visibility is below the minimum reference value, and the non-saturation area corresponds to a remaining area except the shadow area and the saturation area.
 17. The method of claim 15, wherein sum of the height weights with respect to the plurality of directions is equal to 1, and wherein the height at each position is calculated by summing the weight heights with respect to the plurality of directions.
 18. The method of claim 15, further comprising measuring a three dimensional shape by combining the height at each position. 